In Carrier Determined Tolerance, a hapten bound to a non-immunogenic carrier (DNP-isologous IgG), when administered to an animal induces tolerance to the hapten persists on the surface of antigen binding cells, but not in animals injected with DNP-KLH or non-tolerogenic DNP-IgG conjugates. These hapten bearing cells may be the "Tolerant Cell" whose existence has been a source of controversy in immunology. The objective of the proposed research is to study the significance, characteristics, and function of the hapten bearing cell in tolerance. To determine if the cell is responsible for tolerance, we will see if deletion of the cell reverses tolerance. By stripping the hapten from the surface, we will see if the cell functions through receptor blockage or through intracellar mechanisms. By performing double staining for T cells with Rhodamine and hapten bearing cells with Fluorescein, we will determine the cellular origin of the hapten bearing cell. The hapten bearing cell will be isolated on immunoabsorbent columns and placed in culture with normal cells to determine if it is a suppressor cell. Also, the relevance of the hapten bearing cell to self tolerance will be investigated in (NZB X NZW) F1 mice.